Experimental Investigation of Flame Stabilization in a Turbulent Premixed Recirculation-Stabilized Jet-Flame with Simultaneous kHz Laser Diagnostics

摘要

A turbulent premixed recirculation-stabilized jet-flame was investigated experimentally at atmospheric conditions in an optically accessible combustion chamber. The fuel was methane and the perfectly premixed stoichiometric air/methane mixture was preheated to 473 K. The jet exit velocity was 20 m/s corresponding to a Reynolds number of 5600. Simultaneous high-speed laser diagnostic measurements of stereoscopic Particle Image Velocimetry (PIV), OH* chemiluminescence (OH*-CL) from perpendicular directions and Laser Induced Fluorescence of the OH radical (OH-LIF) have been performed at a repetition rate of 5 kHz to visualize and investigate the flame stabilization mechanism qualitatively. Averaged results of the flow velocity field (PIV), the flame shape and position (OH*-CL) and the temperature distribution (OH-LIF) have been analyzed as well as time series of simultaneous single shots. It was found that a combination of several phenomena supports flame stabilization: A consecutive flame front wrap-up at the flame root was identified as a main stabilization source. This process is preceded by spontaneous events of autoignition in the mixing layer between jet and exhaust gas prior to the flame root. Downstream of the autoignition and flame wrap-up events the flame fronts propagate into the jet flow but are constantly washed away. High strain rates due to velocity gradients have been found to inhibit reactions close to the nozzle exit. Spectral analyses showed that none of these processes occur at a dominant frequency.